I would only drill a hole I'n the rear transom area about 2 foot or so off the transom wall and about 3" above the floor into the
Side of the stringer , if you have supertrapps exhaust tips I would remove center nut and investigate the seal ring and look for
Possible entry , more hole u drill the more u weaken the stringer and more filling you have to do ..
When I did mine I also took a pick and dug into the hole and removed the the wood to feel for wetness ...

Little did I know I opened the main valve for the nasty ass water ! Lol

When you fill the holes back up if the wood is dry then mix up some strands of CSM (chopped strand mat)
And silica to thicken like a peanut butter consistency ,, I use more silica , and then take a sandwich bag and fill it with your filler
Cut corner off and squeeze into hole and fair it out smooth .. Don't be frightened of stringers going bad ...

I'm 26 and have never played with wood to this extent ..
.. It is a great thing to concur and alot of beer !!